Just when you least expect it...
What is the difference between criticism from a friend or colleague and a Narcissist's attack? Most people who want to help you, who care for you, will be polite and broach the subject of an injury or insult with care. A Narcissist doesn't want to warn you, because they don't want you to be prepared, they go for the jugular, jumping on whatever insult they feel you have given them, not letting you explain or prepare a defense. They are not 'polite' though they will protest they are the most polite people in the word; their actions give them away.
The attack of a Narcissist is usually unexpected, abrupt and blind sides you. At some time in the past or present they have been humiliated by something you said, the way you looked at them or even by your achievements (this can be how you look, your house, your vacation and even your intelligence). They keep grievances for a long time, letting them simmer and then springing it on you when you least expect it, or when you are unprepared. (This make take place when you are ill or during the reading of a will, when you find out what you did when you were 6 years old that peeved them.)
You have to pay attention to them, compliment them - they perceive you as a source of narcissistic supply/attention. If not they will make you pay. They keep a list of insults, slights, things you did or didn't do, and when they think you are weak and vulnerable, they will attack you. They are cowards, so don't expect a honest dialogue, instead they will vent their spleen on you, threaten you and make you apologize to them.
You have several choices; you can excuse yourself gracefully, putting them at a disadvantage in the sense that you are noble and open minded compared to them, but it also makes you look weak in their eyes, so be careful how you do this. This diffuses the situation, and it makes you aware that you are dealing with a Narcissist - read the rest of this site for more information.
You can deny everything, because most of it makes no sense to you anyway, being a childish rant. This will probably make them angrier, because you are denying their view point, their mad outlook at life.
Or you can counter attack. The last strategy works only if you know about the N attack before hand. They want you to be unprepared and vulnerable, so that their attack works. If you provoke them on purpose make sure you have lots of facts, figures and witnesses. They will never forgive you for besting them. A narcissist will only allow someone they admire to criticize them. Narcissists will never attack someone they admire - it would be like attack themselves as they project their fantasies onto their hero/mirror. Only when their hero falls into disgrace will you hear them criticize their hero.
After the N attack you may feel horrible, physically abused, because they have taken all the trash in their minds, and dumped it on you. Projecting and transference. Think of a childish tantrum. If you can laugh about the attack, then you are OK. Narcissists make you develop good boundaries and defenses. If you let them get to you, let their words, insults and accusations become more and more real and logical, then they have won. They are trying to instill in you an introject; i.e. doubt, fear and self loathing.
The best thing to do is to laugh at them, in private, because they hate to be ridiculed in public. Think of the tale of the Emperor's new cloths, think also of what the story never tells you, what happened to the little boy? Was he beheaded like critics who peeved the queen in Alice in Wonderland? Narcissists hate to be put on the spot but they love putting others on the spot. They are playing a game, because they are not really hurt, they are protecting their mirror image that they admire, and that you some how tarnished.
Remember, they have no real feelings, it is all an act. They are not 'hurt', their image is damaged. They have no feelings, because if they did they would care about your feelings, which is obvious they don't based on why they attacked you in the first place. Go to Theory of Mind.